Ethnic-specific orthopaedic implants and custom cutting jigs

ABSTRACT

An orthopedic implant comprising: (a) a distal femoral component comprising a first condyle bearing surface having a first profile comprising at least three consecutive arcs of curvature; and (b) a proximal tibial component comprising a first condyle bearing surface having a second profile comprising at least three parallel arcs of curvature.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 16/151,070, filed Oct. 3, 2018, which is a continuation of U.S.patent application Ser. No. 14/734,491 filed Jun. 9, 2015, which is adivisional of U.S. patent application Ser. No. 13/268,262 filed Oct. 7,2011, which claims the benefit of U.S. Provisional Patent ApplicationSer. No. 61/530,177 filed Sep. 1, 2011 and is a continuation-in-part ofU.S. Non-provisional patent application Ser. No. 13/203,012 filed Aug.24, 2011, which is a 371 application of PCT/US2010/025466 filed Feb. 25,2010 and claims the benefit of U.S. Provisional Patent Application Ser.No. 61/222,560 filed Jul. 2, 2009 and U.S. Provisional PatentApplication Ser. No. 61/208,509 filed Feb. 25, 2009, the disclosure ofeach of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present disclosure relates to orthopaedic implants and orthopaediccutting jigs and, more specifically, to methods and devices utilized todesign orthopaedic implants and orthopaedic jigs for use with jointreplacement and revision procedures.

INTRODUCTION TO THE INVENTION

Of primary interest to the knee prosthetics industry is the analysis ofthe intrinsic shape differences of the knee joint between differentethnic populations for development of implantable orthopaedic devices.The study presented is thus three-fold: by developing a novel automaticfeature detection algorithm, a set of automated measurements can bedefined based on highly morphometric variant regions, which then allowsfor a statistical framework when analyzing different populations' kneejoint differences.

Ethnic differences in lower limb morphology focus on the differencesbetween Asian and Western populations because this variation is of greatimport in implant design. For example, Chinese femora are moreanteriorly bowed and externally rotated with smaller intramedullarycanals and smaller distal condyles than Caucasian femora. Likewise,Caucasian femora are larger than Japanese femora in terms of length anddistal condyle dimensions. Ethnic differences in proximal femur bonemineral density (BMD) and hip axis length also exists between AmericanBlacks and Whites. The combined effects of higher BMD, shorter hip axislength, and shorter intertrochanteric width may explain the lowerprevalence of osteoporotic fractures in Black women compared to theirWhite counterparts. Similarly, elderly Asian and Black men have beenfound to have thicker cortices and higher BMD than White and Hispanicmen, which may contribute to greater bone strength in these ethnicgroups. In general, Blacks have thicker bone cortices, narrowerendosteal diameters, and greater BMD than Whites. Interestingly, though,these traits are most pronounced in African Blacks compared to AmericanBlacks.

The following analysis considers metric and geometric morphometricvariation in the lower limb of modern American Blacks, Whites and EastAsians. Three-dimensional statistical bone atlases are used in order tofacilitate rapid and accurate data collection in the form of automatedmeasurements, as well as measurements used in biomedical studies andsome newly-devised measurements. The shape analysis is conducted with astatistical treatment combining Principal Components Analysis (PCA) andMultiple Discriminant Analysis; metric analysis is performed usingt-tests, power tests, and linear discriminant analysis in the ImplantDesign and Analysis Suite (see co-pending U.S. patent application Ser.No. 12/673,640, entitled, IMPLANT DESIGN ANALYSIS SUITE, the disclosureof which is incorporated herein by reference) system. The results ofthese analyses add to the existing knowledge of morphological variationin the knee joint and provide useful information that can be extractedfor knee prosthesis design as will be outlined in the remainder of thisdisclosure.

The instant approach may make use of Computed Tomography (CT) scans fordata collection combined with the computational power and precisionoffered by statistical bone atlases. An exemplary data set thatcomprises 943 male and female individuals (81.5% American White, 9%American Black and 9.5% East Asians, where the overall male/female ratio65/35%) was scanned using CT scans. Only normal femora and tibia wereincluded in this study; femora or tibia with severe osteophytes andother abnormalities were specifically excluded. Only one femur and tibiawas chosen from each individual, with no preference taken to eitherright or left side.

The bones were CT scanned using 0.625 mm×0.625 mm×0.625 mm cubic voxels.The result is high resolution, three dimensional radiographs in the formof DICOM image slices. This stacked image data was then segmented andsurface models were generated. This process has been found to bereliable with negligible inter- and intra-observer error. These modelswere then added to the ethnicity-specific statistical bone atlases.

Briefly, a bone atlas is an average mold, or template mesh, thatcaptures the primary shape variation of a bone and allows for thecomparison of global shape differences between groups or populations.Bone atlases were developed initially for automatic medical imagesegmentation; however, it can be used as a way to digitally recreate abone and conduct statistical shape analyses. In addition, bone atlaseshave proven useful in biological anthropology as a means of studyingsexual dimorphism and for reconstructing hominid fossils and makingshape comparisons among fossil species.

For the ethnicity difference analysis, a previously developed techniquefor creating a statistical representation of bone shape was employed ina novel manner. Three separate statistical atlases of femora werecompiled with one atlas containing only American White femora, one atlascontaining only American Black femora, and one atlas containing onlyEast Asian femora. Likewise, three separate atlases were created for thetibia and divided in the same manner (i.e., American White, Black tibiaeand East Asians). The processes of creating these statistical atlasesand adding bones to the atlases are outlined hereafter.

First, all of the bone models in the dataset were compared, and a bonemodel with average shape characteristics was selected to act as atemplate mesh. The points in the template mesh were then matched tocorresponding points in all of the other training models. This ensuresthat all of the bones have the same number of vertices and the sametriangular connectivity. Next, a series of registration and warpingtechniques was used to select corresponding points on all the other bonemodels in the training set. This process of picking pointcorrespondences on new models to be added to the atlas is ‘non-trivial’.The matching algorithm described hereafter uses several well-knowntechniques of computer vision, as well as a novel contribution for finalsurface alignment.

During the first step in the matching algorithm, the centroids of thetemplate mesh and the new mesh were aligned, and the template mesh waspre-scaled to match the bounding box dimensions of the new mesh. Second,a rigid alignment of the template mesh to the new mesh was performedusing a standard vertex-to-vertex Iterative Closest Point (ICP)algorithm. Third, after rigid alignment, a general affine transformationwas performed without iteration. This method was applied to align thetemplate mesh to the new mesh using 12 degrees of freedom (includingrotations, translations, scaling, and shear). After the affinetransformation step, the template and new model have reached the limitsof linear transformation, but local portions of the models still remainsignificantly distant. Since the goal of final surface-to-surfacematching is to create new points on the surface of the new model thatwill have similar local spatial characteristics as the template model, anovel non-linear iterative warping approach was developed to reducemisalignment.

To achieve point correspondence, an iterative algorithm is used wherethe closest vertex-to-vertex correspondences are found from the templateto the new model as before, but now the correspondences from the newmodel to the template model are also found. Using both of these pointcorrespondences, points on the template mesh are moved toward locationson the new mesh using a non-symmetric weighting of the vectors ofcorrespondence. Next, a subroutine consisting of an iterative smoothingalgorithm is applied to the now-deformed template mesh. This smoothingalgorithm seeks to average the size of adjacent triangles on thetemplate mesh, thereby eliminating discontinuities. At the beginning ofthe warping algorithm, the smoothing algorithm uses the actual areas ofthe surrounding triangles to dictate the smoothing vector applied toeach point, which aids in effectively removing outlying points withlarge triangles. Consequently, at the beginning of the process, thetemplate mesh makes large steps, and larger smoothing is required.Toward the end of the process, however, the smoothing vector isnormalized by the total area of the surrounding triangles, which allowsfor greater expansion of the template mesh into areas of high curvature.After this procedure has been completed on all the femora and tibiae intheir respective atlases, the atlases are ready for morphological shapeanalyses and automated metric comparisons.

An innovative statistical treatment was used to analyze global shapedifferences between the two groups. This method utilizes the power of(linear and nonlinear) PCA both as a means of variable reduction and asa global shape descriptor. This method is designed to find points ofhigh discrimination between different gender and/or different ethnicgroups when normalized against the first principal component (PC), whichis considered primarily to scale. This procedure highlights areas onmodels that would be highly discriminating without the use of any otherinformation. The landmarks identified by this algorithm provide adequatediscrimination without the use of any other landmarks between ethnicgroups. This feature finder algorithm is used to examine femoral andtibial shape differences independent of the size differences betweenAmerican Whites, Blacks and East Asians.

A wide array of comparisons was made using specific measurements atdefined landmarks on the ethnicity-specific statistical atlases. Theselandmarks were chosen based on surgical importance, clinical relevance,and historical measurements. Since the atlas consists of homologouspoints on each femur or tibia model, it provides ample information forautomating this process. Also, each bone model in the atlas is alignedto the same coordinate frame. A total of 99 femur and 23 tibiameasurements, angles, and indices were calculated. Furthermore, forpurposes of brevity, only the most significant metric properties arediscussed in the results section. Unless otherwise specified, themeasurements outlined below represent three dimensional (3D) Euclideandistances between pairs of landmarks, and angles are measured as 3Drotations between vectors. In some instances these measurements wereprojected onto a plane for comparison with previous work in the field.

The ordered series of methods used pursuant to the instant disclosureevidenced significant global differences among sex and race, whichsubsequently allowed for isolation of regions likely to be highlydifferent using the feature finder method, and finally allowed for thecoding of algorithms to locate and measure surgically relevant anatomicfeatures with a high degree of accuracy and repeatability. Bones withdifferent scales were considered to have the possibility of shapechanges dependent on size. In this way, correlations between measuredvariables and size were removed in order to expose demonstrable shapedifferences inherent to the ethnicities.

The inventor has used the foregoing analysis to determine that AmericanBlacks have longer, straighter femora with narrower knees than AmericanWhites. In addition, this analysis revealed differences in thedimensions and orientation of the lateral condyle that result in overallshape differences in the distal femur: American Blacks have atrapezoidal-shaped knee, and American Whites have a more square-shapedknee. For each group, the differences in the distal femur are echoed inthe adjacent tibia, whereby American Blacks have a longer lateral tibialcondyle. The mean medial-lateral length of the tibial plateau isslightly longer in Blacks than in Whites, but this difference was notoverly significant given the sample size. However, American Blacks dohave significantly longer and more robust tibiae. In this study, majorshape difference was found between East Asian population and bothAmerican whites and American blacks.

Although racial differences in lower limb morphology are apparent andregister statistically significant, there may be more statistical noisein the American Black sample versus the American White sample. Thisnoise may be a result of the combined effects of genetic admixture sincetheir arrival in the United States, as well as relaxed selection in amore temperate environment. Nonetheless, as discussed earlier, theeffects of admixture have not erased the distinctive morphologicaldifferences between these subgroups of the American population.

In order, to understand normal knee joint kinematics, one must firstunderstand the anatomy of the articulating surfaces of the knee joint.The knee joint is the articulation of the two largest bones in the humanlower extremity, the tibia and the femur. The articular surfaces at theknee joint consists of the curved surfaces that form the lateral andmedial condyles of the distal portion of the femur and are in contactwith the lateral and medial tibial plateaus of the proximal portion ofthe tibia.

The femoral condyles blend into an anterior groove, the trochlea, whichis the articulation for the patella or kneecap. The tibial plateaus areseparated by an intercondylar eminence, which serves as an attachmentpoint for the anterior cruciate ligament and the menisci. The tibialplateaus are also asymmetric, with the lateral plateau the smaller ofthe two. Anatomical studies of the femorotibial articulation have shownthat the medial compartment has greater contact area than the lateralcompartment.

The fibula is attached to the tibia's lateral side by a dense membranealong its length and at the ends by cartilaginous joints supported byligaments. The connection of the bones permits very little relativemovement. The proximal tibia-fibular joint is below the level of thetibio-femoral articulation, while the distal ends of the two bones formthe proximal end of the ankle joint.

In the normal knee, posterior femoral rollback during an increasingflexion routinely occurs. Greater amounts of posterior femoral rollbackhave been observed during activities requiring greater magnitudes offlexion such as a deep knee bend maneuver. Posterior rollback issubstantially greater at the lateral femorotibial articulation thanmedially, therefore creating a medial pivot type of axial rotationalpattern in which the tibia internally rotates relative to the femur asflexion increases. Numerous kinematic evaluations have found a similarpattern and magnitude of posterior femoral rollback during deep flexionactivities. This differs somewhat from axial rotational patternsobserved after total knee arthroplasty (TKA), which showed lowermagnitudes of axial rotation and occasional pathologic rotationalpatterns such as lateral pivot rotation and reverse screw-home rotation(tibia externally rotating relative to the femur with increasingflexion).

Also, the anterior translation of the femur on the tibia observed afterTKA has numerous potential negative consequences. First, anteriorfemoral translation results in a more anterior axis of flexion,lessening maximum knee flexion. Second, the quadriceps moment arm isdecreased, resulting in reduced quadriceps efficiency. Third, anteriorsliding of the femoral component on the tibial polyethylene (PE) surfacerisks accelerated PE wear.

A primary objective of TKA should be to reproduce the kinematics of anormal knee. At present, this objective is largely overlooked. Numerousin vivo, weight bearing, and fluoroscopic analyses have shown thatnormal knee kinematics are difficult to obtain after TKA using existingorthopaedic implants. Multiple kinematic abnormalities (reducedposterior femoral rollback, paradoxical anterior femoral translation,reverse axial rotational patterns, and femoral condylar lift-off) arecommonly present. Understanding these kinematic variances assisted indesign of better TKA implants, which work toward reducing andeliminating these kinematic abnormalities or at least accommodating themwithout creating adverse conditions that limit implant performance orlongevity. Most of the knee implants are off-the shelve-knee systems,which are designed for average motion—not patient specific kinematics.Accordingly, TKA motion and kinematics of the knee that areindistinguishable from a normal knee should utilize customization foreach patient. Currently, customization is a difficult task, but theinstant disclosure addresses this customization, in part, by offering adeformable articulating template (DAT) methodology described hereafter.

For purposes of the instant disclosure, radius of curvature is theradius of a circle having a circumferential curvature that approximatesthe curvature of a rounded object. For example, the radius of curvatureis infinite for a straight line, while the radius of decreases frominfinity as the curvature increases. In particular, the radius ofcurvature for a smaller circle is less than the radius of curvature fora larger circle because the curvature of the smaller circle is greaterthan the curvature of the larger circle. Simply put, the smaller theradius of curvature, the larger the curvature.

The inventor has found that one may map and simulate the curvature ofthe natural knee condyles by applying two or more radii of curvaturealong the camming surfaces from anterior to posterior. In particular, ithas been found that for the Caucasian population, five distinct radii ofcurvature closely track the curvature of the camming surfaces of thecondyles from anterior to posterior. Moreover, it has been found thatasymmetry in the radii of the curvature of the condyles is responsiblefor imposing an internal rotation of the tibia with respect to the femurduring flexion. Beyond 20° of flexion, sliding motion begins on bothcondyles.

Extension of the knee joint produces a coupled external rotation of thetibia with respect to the femur; this rotation has been described as the“screw-home” movement of the knee. This screw-home movement is due tothe existence of a larger area of bearing surface on the medial condylethan on the lateral condyle. When the whole articular surface of thelateral condyle has been used up, the femur rotates around the tibialspine until the joint is screwed home or close packed in extension. Asthe knee joint flexes and extends, this rotation causes the tibialmotion on the femur to assume a spiral or helicoid form that resultsfrom the anatomical configuration of the medial femoral condyle. As thetibia slides on the femur from the fully extended position, it descendsand ascends the curves of the medial femoral condyle and simultaneouslyrotates externally. This motion is reversed as the tibia moves back intothe fully flexed position. The screw-home mechanism gives more stabilityto the knee in any position than would be possible if the femorotibialjoint was a pure hinge joint.

The meniscal cartilages (menisci) between the femoral condyles and thetibial articular surfaces are two crescentic fibrocartilage structuresthat serve to deepen the articular surfaces of the tibia for receptionof the femoral condyles. On cross-section, the menisci have a wedge-likeappearance. The menisci perform several important functions, including(1) load transmission across the joint, (2) enhancement of articularconformity, (3) distribution of the synovial fluid across the articularsurface, and (4) prevention of bone impingement during joint motion.When the menisci are present, the load-bearing area for each condyleapproximates 6 cm², but this surface area decreases to approximately 2cm² when the menisci are damaged or severely degraded. Therefore, whenthe effective area of load bearing is increased, the stress transferredto the cartilages is reduced and vice versa.

In the normal knee joint, the anterior cruciate ligament (ACL) and theposterior cruciate ligament (PCL) are intrinsic, lying inside the jointin the intercondylar space. These ligaments control theanterior-posterior and axial rotational motion in the joint. Theanterior cruciate ligament provides the primary restraint for anteriormovement of the tibia relative to the femur while the posterior cruciateligament offers the primary restraint to posterior movement of thetibia, accounting for over 90% of the total resistance to this movement.

The morphologic shape of the distal femur should dictate the shape,orientation, and kinematics of the prosthetic replacement used for TKA.Traditional prosthetic designs incorporate symmetric femoral condyleswith a centered trochlear groove. Traditional surgical techniques centerthe femoral component to the distal femur and position it relative tovariable bone landmarks. However, documented failure patterns andkinematic studies demonstrate how traditional design and surgicaltechniques reflect a poor understanding of distal femoral morphology andknee joint kinematics, in addition to a disregard for the patella andits tracking of the distal femur.

The trochlea is designed to guide and hold the patella. Patella trackingis influenced by many different factors: the geometry of the trochleargroove, the geometry of the posterior side of the patella, soft tissueextensor mechanism and the orientation of the tibia. The normal movementof the patella on the femur during flexion is a vertical displacementalong the central groove of the femoral patellar surface down theintercondylar notch. The geometry of the trochlear groove and theposterior side of the patella constrains patella tracking, particularlyat high flexion angles. The patella is held centrally by the conformityof the facets with the sulcus of the femur and by the patellofemoralligaments. These ligaments represent a conformation of the capsule intothickened structures on the medial and lateral side of the patella.These ligaments are located superiorly and inferiorly on either side,and extend from the anterior surface of the patella posteriorly to theside of each femoral condyle. These ligaments also constrain the motionof the patella, but can be overruled by the sulcus constraints or byexternal forces. In a normal knee it is acceptable to presume that thetracking of the patella will be very similar to the orientation of thetrochlea. As a result, the orientation of the trochlear groove of a kneeprosthesis should be similar to the orientation of the natural trochleato reproduce this natural patella track.

In sum, the knee joint is an example of very well balanced system. Aslight change within this system, affects the whole system. Changeswithin the patella-femoral joint can have considerable long termeffects, as the transmitted forces within this part of the knee jointare relatively high. TKA easily induces changes within thepatella-femoral joint. At present, the simulated trochlear grooveorientation of TKA components does not conform to the natural trochlearorientation. Accordingly, the groove orientation of future femoralcomponents should incorporate a trochlear groove that simulates thenatural orientation of the trochlear groove of a natural femur.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram showing how an exemplary software packagegenerates a prosthetic implant design.

FIG. 1B is a schematic depicting an exemplary process flow forgeneration of a patient specific prosthetic implant.

FIG. 2 is a schematic diagram showing a statistical atlas overview.

FIG. 3 is a schematic diagram showing a two step feature extractionprocess carried out by the exemplary software package.

FIG. 4 is a distal view of a femur showing certain anatomicmeasurements.

FIG. 5 is a proximal view of a tibia showing certain anatomicmeasurements.

FIG. 6 is a series of distal views of six femurs showing variousclassification in accordance with the instant disclosure.

FIG. 7 is a plot showing femoral AP length as a function of ML lengthfor male and female Asians, African Americans, and Caucasians.

FIG. 8 is a plot showing tibial AP length as a function of ML length formale and female Asians, African Americans, and Caucasians.

FIG. 9 is a depiction of Caucasian male and female femur size clustersclassified by AP and ML dimensions.

FIG. 10 is a depiction of Caucasian male and female tibia size clustersclassified by AP and ML dimensions.

FIG. 11 is a series of Caucasian distal femur templates (male andfemale) in accordance with the instant disclosure.

FIG. 12 is an Asian female distal femur template in accordance with theinstant disclosure.

FIG. 13 is an African-American male distal femur template in accordancewith the instant disclosure.

FIG. 14 is an elevated perspective view of a distal femur of an Asianshowing the articulating surface approximated by three curves (percondyle).

FIG. 15 is an elevated perspective view of a distal femur of a Caucasianshowing the articulating surface approximated by four curves.

FIG. 16 is an elevated perspective view of a distal femur of anAfrican-American showing the articulating surface approximated by fourcurves.

FIG. 17 is a distal view and a profile view of a point cloudrepresentative of a distal femur articulating surface generated by arotating chopper about the transepicondylar axis.

FIG. 18 is an elevated perspective view and an overhead view of atrochlear groove point cloud generated by a horizontal chopper.

FIG. 19 is an elevated perspective view of the chopper chopping a distalfemur about the transepicondylar axis and the resulting implantarticulating surfaces.

FIG. 20 is a frontal view of an Asian female template and an elevatedperspective view of a total femoral implant generated using thetemplate.

FIG. 21 is a frontal view of an African-American male template and anelevated perspective view of a total femoral implant generated using thetemplate.

FIG. 22 is a frontal view of a Caucasian male template and an elevatedperspective view of a total femoral implant generated using thetemplate.

FIG. 23 is a frontal view of a Caucasian female template and an elevatedperspective view of a total femoral implant generated using thetemplate.

FIG. 24 is a frontal view of a posterior stabilized total femoralimplant fabricated in accordance with the instant disclosure.

FIG. 25 is an elevated perspective view of a Caucasian male partialfemoral implant fabricated in accordance with the instant disclosure.

FIG. 26 is an elevated perspective view from the front and rear of aCaucasian male unilateral femoral implant fabricated in accordance withthe instant disclosure.

FIG. 27 is an elevated perspective view from the front and rear of anAfrican-American male unilateral femoral implant fabricated inaccordance with the instant disclosure.

FIG. 28 is a rear, overhead view of a femoral prosthetic componenthaving a rectangular inner surface.

FIG. 29 is a rear, overhead view of a femoral prosthetic componenthaving a trapezoidal inner surface.

FIG. 30 is an overhead view of a proximal tibial template for an Asianmale.

FIG. 31 is an overhead view of a proximal tibial template for anAfrican-American female.

FIG. 32 is an overhead view of a proximal tibial template for aCaucasian male.

FIG. 33 is a profile view of a proximal tibial template for anAfrican-American female, shown with the resection plane.

FIG. 34 is an overhead view of the proximal tibial template for anAfrican-American female, with data points corresponding to theperipheral areas of the tibial template contacted by the resectionplane.

FIG. 35 is a parameterized resection profile of a tibial template.

FIG. 36 is an overhead view of a Caucasian male tibial implant.

FIG. 37 is an overhead view of an African-American female tibialimplant.

FIG. 38 is an overhead view of an Asian male tibial implant.

FIG. 39 is an overhead view of a articulating surface point cloud for aproximal tibia divided into six regions.

FIG. 40 is shows a curve parameterizing the contour of tibia surfaceregion 1 of FIG. 39 .

FIG. 41 is shows a curve parameterizing the contour of tibia surfaceregion 2 of FIG. 39 .

FIG. 42 is shows a curve parameterizing the contour of tibia surfaceregion 3 of FIG. 39 .

FIG. 43 is shows a curve parameterizing the contour of tibia surfaceregion 4 of FIG. 39 .

FIG. 44 is shows a curve parameterizing the contour of tibia surfaceregion 5 of FIG. 39 .

FIG. 45 is shows a curve parameterizing the contour of tibia surfaceregion 6 of FIG. 39 .

FIG. 46 is an elevated perspective view of a tibial tray insertgenerated from the parameterized curves of FIGS. 40-45 .

FIG. 47 is an elevated perspective view of a tibial tray insert for acruciate retaining knee system generated from the parameterized curvesof FIGS. 40-45 .

FIG. 48 is an elevated perspective view of a tibial tray insert for aposterior stabilized knee system generated from the parameterized curvesof FIGS. 40-45 .

FIG. 49 is an elevated perspective view of a medial tibial bearinginsert and a lateral tibial bearing insert generated from theparameterized curves of FIGS. 40-45 .

FIG. 50 is an elevated perspective view of a medial tibial bearinginsert generated from the parameterized curves of FIGS. 40-45 .

FIG. 51 is an elevated perspective view of a lateral tibial bearinginsert generated from the parameterized curves of FIGS. 40-45 .

FIG. 52 a schematic diagram of a patient specific implant generationsequence in accordance with the instant disclosure.

FIG. 53 is an elevated perspective view of a distal femur shown withcartilage prior to contoured resection.

FIG. 54 is an elevated perspective view of an anterior and a posteriordistal femur shown without cartilage subsequent to contoured resection.

FIG. 55 is an elevated perspective view of an exemplary resection guidein accordance with the instant disclosure.

FIG. 56 is an elevated perspective view of a second exemplary resectionguide and microsurgical robot in accordance with the instant disclosure.

FIG. 57 is a schematic diagram of a system overview for constructing apatient specific cutting jig.

FIG. 58 is a schematic diagram of the patient specific cutting toolcreation module of FIG. 57 .

FIG. 59 is a profile view of an exemplary anterior-posterior cuttingguide showing traversal of a medial-lateral cutting guide along theanterior-posterior cutting guide in the anterior-posterior direction.

FIG. 60 is a rear view of the exemplary anterior-posterior cutting guideand medial-lateral cutting guide, showing traversal of a cutting devicein the medial-lateral direction along the medial cutting guide.

FIG. 61 is an anterior and a posterior view of a distal femur aftermedial cartilage removal.

FIG. 62 is an anterior and a posterior view of a distal femur afterlateral cartilage removal.

FIG. 63 is an anterior and a posterior view of a distal femur aftermedial and lateral cartilage removal.

FIG. 64 is an elevated perspective view of an exemplary base and anexemplary position jig for the base.

FIG. 65 is an elevated perspective view of the base and position jig ofFIG. 64 mounted together, and an elevated perspective view of the baseand position jig of FIG. 64 contacting a distal femur.

FIG. 66 is an elevated perspective view of the base and position jig ofFIG. 64 contacting a distal femur, and two screws operative to mount thebase to the distal femur without reliance upon the position jig forattachment.

FIG. 67 is an elevated perspective view of the base mounted to thedistal femur, where the base is mounted to an arm using a set screw.

FIG. 68 is an elevated perspective view of the base mounted to thedistal femur, where the base is mounted to the arm, which is mounted tothe anterior-posterior cutting guide, which is mounted to the medialcutting guide.

FIG. 69 is an elevated perspective view of the base mounted to thedistal femur, where the base is mounted to the arm, which is mounted tothe anterior-posterior cutting guide, which is mounted to the lateralcutting guide.

FIG. 70 is an elevated perspective view of the base mounted to thedistal femur, where the base is mounted to the arm, which is mounted tothe anterior-posterior cutting guide, which is mounted to the anteriorcutting guide.

FIG. 71 is an anterior view showing the profile of the medial condyle,the lateral condyle, and the sulcus for the same distal femur.

FIG. 72 is a schematic diagram for generation of the medial AP cuttingguide.

FIG. 73 is a profile view of a set of points representative of thecurvature of a medial condyle for a distal femur and the profile contourcurve that results from fitting a line to the set of points.

FIG. 74 is a profile of a medial condyle of a distal femur along withanterior sulcus profile lines used to fabricate the medial AP cuttingguide.

FIG. 75 is a profile of a medial condyle of a distal femur that includesthe posterior section defined by the condyle profile and the anteriorsection defined by the sulcus profile, both of which are used tofabricate the medial AP cutting guide.

FIG. 76 is an elevated perspective view of the medial AP cutting guidepositioned to the side of a distal femur from which the profile for themedial AP cutting guide was generated.

FIG. 77 is a schematic diagram for generation of the lateral AP cuttingguide.

FIG. 78 is a profile view of a set of points representative of thecurvature of a lateral condyle for a distal femur and the lateral APcutting guide that results from matching the curvature of the lateralcondyle.

FIG. 79 is an elevated perspective view of the lateral AP cutting guidepositioned to the side of a distal femur from which the profile for thelateral AP cutting guide was generated.

FIG. 80 is a schematic diagram for generation of the anterior AP cuttingguide.

FIG. 81 is a profile view of a set of points representative of thecurvature of an anterior portion of a distal femur and the resultingcontour of the anterior AP cutting guide.

FIG. 82 is a profile view of the curvature defining the anterior APcutting guide shown with the points representative of the sulcuscurvature.

FIG. 83 is an elevated perspective view of the anterior AP cutting guidepositioned to the side of a distal femur from which the profile for theanterior AP cutting guide was generated.

FIG. 84 is a schematic diagram for generation of the ML cutting guides.

FIG. 85 is an elevated perspective view of a distal femur after achopper has been rotated about the TEA, where the points representsurface points that collectively provide a contour profile for theexterior of the distal femur.

FIG. 86 is an elevated perspective view of a distal femur after achopper has been rotated about the TEA, where the points representsurface points that collectively provide a contour profile forfabrication of the anterior ML cutting guide.

FIG. 87 is an elevated perspective view of a distal femur after achopper has been rotated about the TEA, where the points representsurface points that collectively provide a contour profile forfabrication of the medial ML cutting guide and the lateral ML cuttingguide.

FIG. 88 are elevated perspective views of the same distal femur, shownwith data points on the left corresponding to the contour of the lateralML cutting guide and data points on the right corresponding to the countour of the medial ML cutting guide.

FIG. 89 is a view of the data points of FIG. 88 being rotated about theTEA to create a series of flat planes.

FIG. 90 shows the planes of FIG. 89 after the planes are stacked in themedial-to-lateral direction.

FIG. 91 is a resultant line representing the anterior contour of thestacked planes of FIG. 93 , which comprises part of the resultantcontour of the ML cutting guides.

FIG. 92 is a view of the data points of FIG. 91 being rotated about theTEA to create a series of flat planes.

FIG. 93 shows the planes of FIG. 92 after the planes are stacked in themedial-to-lateral direction.

FIG. 94 is a resultant line representing the medial and lateral contoursof the stacked planes of FIG. 93 , which comprises part of the resultantcontour of the ML cutting guides.

FIG. 95 is a profile view of a medial ML cutting guide shown with themedial contour curve used to fabricate the medial ML cutting guide.

FIG. 96 is an elevated perspective view of a medial ML cutting guide.

FIG. 97 is a profile view of a lateral ML cutting guide shown with thelateral contour curve used to fabricate the lateral ML cutting guide.

FIG. 98 is an elevated perspective view of a lateral ML cutting guide.

FIG. 99 is a profile view of an anterior ML cutting guide shown with theanterior contour curve used to fabricate the anterior ML cutting guide.

FIG. 100 is an elevated perspective view of an anterior ML cuttingguide.

FIG. 101 is an elevated perspective view of a carriage assembly, shownby itself and mounted to a AP cutting guide.

FIG. 102 is a profile view of the carriage assembly of FIG. 101 , shownat the ends of the range of motion available for a particular AP cuttingguide.

FIG. 103 is an anterior view of a distal femur having mounted to it abase, an arm, an AP cutting guide, and a medial ML cutting guide.

FIG. 104 is an anterior view of a distal femur having mounted to it abase, an arm, an AP cutting guide, and a lateral ML cutting guide.

FIG. 105 is an anterior view of a distal femur having mounted to it abase, an arm, an AP cutting guide, and an anterior ML cutting guide.

FIG. 106 is a profile view of a distal femur having mounted to it abase, an arm, an AP cutting guide, a ML guide, and a microsurgicalrobot, and a repositioning device for removing cartilage from the distalfemur, where the ML guide, the microsurgical robot, and therepositioning device are repositionable along the AP cutting guide.

FIG. 107 is an anterior view of the structure of FIG. 106 , where themicrosurgical robot and the repositioning device are repositionablealong the ML guide.

FIG. 108 is an anterior and profile view of the anterior ML track beforelowering the cutting depth by 1 mm.

FIG. 109 is an anterior and profile view of the anterior ML track afterlowering the cutting depth by 1 mm.

FIG. 110 is a distal view of the anterior ML track after lowering thecutting depth by 1 mm.

FIG. 111 is an initial anterior view and distal view of medial ML and APtracks.

FIG. 112 is an initial posterior view of medial ML and AP tracks.

FIG. 113 is an elevated perspective view showing the sheet body andcartilage cutting body (medial).

FIG. 114 is an anterior view of a distal femur before and after medialcartilage removal.

FIG. 115 is a posterior view of a distal femur before and after medialcartilage removal.

FIG. 116 is an elevated perspective view and s profile view of thelateral ML track before lowering the cutting depth by 2 mm.

FIG. 117 is a distal view of the lateral ML track after lowering thecutting depth by 2 mm.

FIG. 118 is a lateral view and a distal view of the lateral ML trackafter lowering the cutting depth by 2 mm.

FIG. 119 is a posterior view of lateral ML and AP tracks.

FIG. 120 is an elevated perspective view showing the sheet body andcartilage cutting body (lateral).

FIG. 121 is an anterior view of a distal femur before and after lateralcartilage removal.

FIG. 122 is a posterior view of a distal femur before and after lateralcartilage removal.

FIG. 123 is an anterior view of an anterior ML track.

FIG. 124 is a bottom view of an anterior ML track,

FIG. 125 is an elevated perspective view showing the sheet body andcartilage cutting body (anterior).

FIG. 126 is an anterior view of a distal femur before and after anteriorcartilage removal.

FIG. 127 is a bottom view and an elevated perspective view of a combinedcut pathway.

FIG. 128 is an anterior view of a distal femur before and after totalcartilage removal.

FIG. 129 is a posterior view of a distal femur before and after totalcartilage removal.

FIG. 130 is a profile view of a microsurgical robot guide mounted to adistal femur.

FIG. 131 is an anterior view of the microsurgical robot guide of FIG.130 .

FIG. 132 is an elevated perspective view (from lateral) of themicrosurgical robot guide of FIG. 130 , along with a separate elevatedperspective view of an exemplary support frame (shown without the robotand associated equipment).

FIG. 133 is an elevated perspective view (from medial) of themicrosurgical robot guide of FIG. 130 .

FIG. 134 is an elevated perspective view (from lateral) of themicrosurgical robot guide of FIG. 130 .

FIG. 135 is an elevated perspective view (from profile, lateral) of themicrosurgical robot guide of FIG. 130 .

FIG. 136 is an elevated perspective view (from lateral) of themicrosurgical robot guide of FIG. 130 showing the microsurgical robot inan anterior position.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The exemplary embodiments of the present invention are described andillustrated below to encompass prosthetic knee implants, jigs for usewith preparing tissue to receive prosthetic knee implants, and methodsand devices for designing prosthetic knee implants and jigs, as well asmicrosurgical robots for use with the same. Of course, it will beapparent to those of ordinary skill in the art that the embodimentsdiscussed below are exemplary in nature and may be reconfigured withoutdeparting from the scope and spirit of the present invention. However,for clarity and precision, the exemplary embodiments as discussed belowmay include optional steps, methods, and features that one of ordinaryskill should recognize as not being a requisite to fall within the scopeof the present invention.

The following are definitions that relate to axes, landmarks, andmeasurements with respect to the distal femur. These definitions alsogovern the proper construction of these terms as used in the instantdisclosure.

Transepicondylar Axis (TEA)—This measurement is known in theanthropological literature as biepicondylar breadth. To compute theclinical transepicondylar axis (TEA), rough sets of vertices weremanually defined on an average femur on the most lateral prominence ofthe lateral epicondyle and the most medial prominence of the medialepicondyle. This step was only performed once, since vertices in theatlas femora are homologous. Using these rough sets of points, a searchregion of 10 mm radius was defined from the centroid of the rough setsof vertices on both the lateral and medial sides. Defining the vectorfrom each of these centroids then gives a rough direction for the TEA. Apair of points was selected by maximizing the distance in this roughdirection; these selected points form the endpoints of the TEAmeasurement.

Transepicondylar Axis Length (TEAL)—distance between the medial andlateral condyles.

Anteroposterior Height (APH)—distance between anterior cortex points andthe posterior plane.

Medial Anteroposterior Height (MAP)—distance between most anterior andposterior aspects of the medial condyle.

Lateral Anteroposterior Height (LAP)—distance between most anterior andposterior aspects of the lateral condyle.

Anatomic Axis—Distal Axis Angle—angle between anatomic axis and axisconnecting the two most distal points of the medial and lateralcondyles.

Patellar Groove Height (PGH)—distance between aspect of theintercondylar notch and the midpoint between the two most distal pointson the medial and lateral condyles.

Anteroposterior Angle Difference (AP-AD)—angle of the vector connectingthe two most anterior points on the lateral and medial condyles and thevector relative to the posterior plane.

Anterior Mediolateral Length (AML)—distance between the two mostanterior aspects of the medial and lateral condyles.

Posterior Mediolateral Length (PML)—distance between the two mostposterior aspects of the medial and lateral condyles.

Distal Mediolateral Length (DML)—distance between the two most distalaspects of the medial and lateral condyles.

Condylar Twist Angle (CTA)—angle between the transepicondylar axis andposterior condylar axis.

The following are definitions that relate to axes, landmarks, andmeasurements with respect to the proximal tibia. These definitions alsogovern the proper construction of these terms as used in the instantdisclosure.

Mediolateral Width (ML)—maximum width of the tibia plateau in themediolateral direction.

Anteroposterior Height (AP)—length of the tibial plateau in theanteroposterior direction, passing through the midpoint of the tibialintercondylar eminence.

Eminence Mediolateral Ratio (EM_W)—medial plateau mediolateral width tomediolateral width ratio.

Tuberosity Eminence Vector Angle (TEVA)—angle between anteroposteriordirection and a line connecting the intercondylar eminence midpoint andtibial tuberosity.

Lateral Plateau Mediolateral Width (LPW)—length of the lateral tibialplateau in the mediolateral direction.

Lateral Plateau Anteroposterior Height (LPH)—length of the lateraltibial plateau in the anteroposterior direction.

Medial Plateau Mediolateral Height (MPW)—length of the medial tibialplateau in the mediolateral direction.

Medial Plateau Anteroposterior Height (MPH)—length of the medial tibialplateau in the anteroposterior direction.

End of Definitional Section

Morphological differences exist between genders and ethnicities. A firstexemplary embodiment comprises a software package utilizing statisticalbone atlases to define these morphological differences of the knee. Thissoftware package uses the morphological information to create gender andethnic specific mass customized implants, as well as patient specificimplants, for the knee. These knee systems may comprise total cruciateretaining, total posterior stabilized, partial, and unilateral. Theexemplary software package is also capable of analyzing and reshapingexisting knee systems.

Referring to FIG. 1A, an exemplary schematic diagram 100 depicts thehigh level processes carried out by the exemplary software package tocreate mass customized or patient specific orthopaedic implants. Inexemplary form, the software package starts by importing 102 a patientfemur and tibia model for analysis 104 of the articulating geometryaccording to the patient's gender and ethnicity. After the analysis 104of the articulating geometry is carried out, the software packagedetermines 106 whether the patient's bone anatomy fits within a range ofsizes available for a mass customized implant. Thereafter, the processcan go in one of two directions 108, 110: (a) a mass customizedorthopaedic implant; or, (b) a patient specific orthopaedic implant.

In the first direction 108, presuming the patient's bone anatomy fitswithin a range of template sizes available for a mass customized implant112, the software package selects the appropriate template size 114 forthe mass customized implant. For approximately 90% of the population,the patient will fall within the range of template sizes for the masscustomized implant family. Thereafter, the software package processesthe selected template size and modifies the template to have thecontours of the template more closely approximate the contours of thepatient's natural anatomy, whether it is a total femoral 116, a partialfemoral 118, or a unilateral femoral 120, is then selected for thepatient.

Conversely, in the second direction 110 (presuming the patient's boneanatomy does not fit within a range of template sizes available for amass customized implant, or the consulting physician opts for a patientspecific implant over a mass customized implant) and as shown in FIG.1B, the software package analyzes 124 three dimensional bone models ofthe patient's actual femur and tibia (constructed from MRI, CT, X-Ray,etc.) using an arc analysis. Prior to analyzing the patient's actualfemur and tibia, three dimensional virtual bone models are created 111that include models of the patient's current cartilage. In circumstanceswhere the cartilage is degenerative, the software package identifiesthis degeneration 113 and automatically supplements the cartilage modelto create a healthy cartilage model 115. Thereafter, the arc analysis124 identifies and maps the contours of the medial and lateral profilesof the patient's articulating surface, which are parameterized, tocreate a patient specific template 126. This patient specific template126 is then further refined/customized to create 117 a patient specificorthopaedic implant 242 (see FIG. 52 ) (whether total, partial, orunilateral) to fit the patient's needs.

Referring to FIG. 1B, to the extent a partial or unilateral implant isdesired, the full implant model is available to have a surface pointselected, thereby causing the software package to generate 119 areference plane. This reference plane is normal to the surface point onthe model selected and is manipulatable to define the field of view. Inexemplary form, the field of view is manipulated to encompass the areason the implant model that will be used to construct the partial orunilateral implant. Thereafter, in a region isolation step 121, the userof the software package selects the particular portions of the implantmodel that will be used to create the partial or unilateral implant. Thesoftware then automatically extracts these regions and creates 123 astand-alone partial or unilateral implant. Thereafter, the stand-alongimplant is fit 125 onto the dimensional virtual bone models. Thisfitting includes automatic removal of cartilage and possibly some boneas part of an automatic resurfacing that occurs via the softwarepackage. After proper fitting, the stand-alone implant is removed fromthe bone model, thereby leaving behind bone model with a resurfacedportion. This resurfaced portion of the three dimensional bone model isanalyzed 127 by the software package to create three dimensional cuttingdirections (for an automated or computerized cutter) that allow thecutter to resurface the patient's actual bone to accept the fabricatedstand-alone implant.

Referencing FIG. 2 , the imaging modality used to acquire the patientfemur and tibia models that are imported 102 into the software packagemay include, without limitation, one or more of computed tomography(CT), magnetic resonance imaging (MRI), and X-radiation (X-rays). Postimaging of the patient's femur and tibia, an electronic model of thepatient's femur and tibia are then automatically constructed and addedto the software package's bone atlases 130. A bone atlas is an averagemodel that captures the primary shape variations of bones and allows forthe comparison of global shape differences between groups orpopulations. In exemplary form, the software package includes twelveseparate statistical atlases 130 of femora and tibiae (six femora andsix tibiae) are created that correspond to three ethnicities(Caucasians, African Americans, and Asians) and both genders (male andfemale). In other words, the software package includes a separatestatistical atlas for both the femora and the tibia for a maleCaucasian, a female Caucasian, a male African American, a female AfricanAmerican, a male Asian, and a female Asian. By having statisticalatlases 130 that are gender and ethnic specific, the resulting atlastibia and femur are standardized, normalized, and guaranteed to havelandmark correspondence across a population.

Referring to FIG. 3 , a two-step feature extraction methodology 132 isimplemented by the exemplary software package to fully identify shapedifferences among ethnicities. In a first step 134, global shapedifferences between the sexes in each ethnicity and between the sexesacross all ethnicities (in exemplary discussion, three ethnicities) areidentified. This first step 134 makes use of principle componentanalysis, a mathematical tool that reduces the dimensionality ofvariables while maintaining most of the variance of the original data,both as a means of variable reduction and as a global shape descriptor.Principle component analysis is used by the software package to findpoints of high discrimination between different sex and ethnic groupswhen bones falling within these groups are normalized against the firstprincipal component. The first principal component is consideredprimarily scale and is used to highlight highly discriminatory areasbetween a standard bone and the bones falling into the different sex andethnic groups. A principle component analysis algorithm is used by thesoftware package to analyze shape differences (independent of sizedifferences) between the sexes and among the ethnic populations(Caucasians, African Americans, and Asians).

Referring to FIGS. 3-5 , following the first step 134 is a second step136 that utilizes anatomic and surgical landmarks to automaticallycalculate linear measurements, angular measurements, and curvature aftera bone is added to the atlas. In FIGS. 4 and 5 , each of themeasurements taken by the software package for the tibia and femur bonemodels is marked with a corresponding acronym to show precisely thewhere the measurements are taken. It should be noted that themeasurement acronyms were listed in the preceding definitional sectionand reference is had to that section for a more detailed explanation ofeach measurement.

Referencing FIGS. 6-10 , the software package uses six classifications140-150 to describe femoral shape based on three normalized ratios. TypeI 140 and Type II 142 classify femoral shape relative to mediolateralwidth/anteroposterior height (ML/AP), Type III 144 and Type IV 146classify femoral shape relative to anterior mediolaterallength/posterior mediolateral length (AML/PML), and Type V 148 and TypeVI 150 classify femoral shape relative to medial anteroposteriorheight/lateral anteroposterior height (MAP/LAP). By using these sixclassifications 140-150, the software package identifies morphologicaldifferences between ethnicities and gender.

As shown in FIGS. 7 and 8 , plots of measurements taken foranterior-posterior (AP) height and medial-lateral (ML) width of femursand tibiae from various ethnicities (Caucasian, African American, andAsian) and genders confirm that significant morphological differencesexist between each group.

Referring to FIGS. 9, 10, 12 and 13 , the software package was used tocarry out an exemplary analysis of femoral and tibial ML width and APheight dimensions within the Caucasian male and female populations thatyielded six clusters of male and female sizes for a total of twelveCaucasian sizes. In particular, the ML width measurements were plottedagainst AP height measurements which were plotted against a repetition(i.e., frequency corresponding to the number of similarly shaped bones)factor of both measurements in a third dimension to create thethree-dimensional (3D) plots 152, 154 for the femur and tibia. Eachprojection of a 3D plot represented a separate cluster, resulting in sixprojections for both the Caucasian male and Caucasian female. Eachprojection is representative of a separate size. FIGS. 9 and 10 alsoinclude charts 156, 158 numerically detailing the six sizes for bothCaucasian males and females for the femur and tibia. Dimensions (ML, AP)from the remaining ethnicities are also separable and used by thesoftware package to generate 3D plots providing distinct projections(also referred to herein as “clusters”) that correspond to distinctsizes for a respective profile (ethnicity and gender, such as Asianfemale). The software package then generates an average bone model foreach projection, where the average bone model represents the average ofall of the bones that fall within the projection. This average bonemodel is referred to herein as a template 160.

Referencing FIGS. 11-13 , the software package uses the results of theshape analysis for each ethnicity and gender to create a series of masscustomized implant families 162 by using the template bone 160 to createthe mass customized implant for that cluster. When a patient is to befit with a mass customized implant, his/her bone is added to the atlas130 and classified to assign the bone to a particular cluster. In thismanner, the mass customized implant of the assigned cluster is thenassociated/assigned to the patient.

Referring to FIGS. 1 and 14-16 , the exemplary software package utilizesa curvature analysis process 124 to create the mass customized implantsand patient specific implants. In exemplary form, the curvature analysis124 is applied to each template femur 160 and each template tibia 160within the atlas to generate the profile and curvature for thosetemplates. In contrast, for a patient specific implant, the curvatureanalysis is applied directly to the patient's femur and tibia models togenerate the patient specific profiles and curvature after the patient'sfemur and tibia models have been added to the atlas 130.

To generate the femur template curvature, the femoral surface isanalyzed by the software package's atlas 130 to define the medial andlateral curvature profiles as well as the curvature of the distal femurtemplate 160. The medial curvature profile 164 is defined by a planecreated by the medial anterior point (most anterior point in medialcondyle), the medial distal point (most distal point on medial condyle),and the medial posterior point (most posterior point in medial condyle).A contour profile is then generated that corresponds to the most outwardprotruding points on the medial condyle surface where this planeintersects the distal femur. A contour profile 166 is also generatedthat corresponds to the most outward protruding points on the lateralcondyle surface where this plane intersects the distal femur. Theresulting contour profiles 164, 166 for the medial and lateral condylesdo not exhibit uniform curvature. Rather, to match the overall contourprofile a series of curves are required to approximate the medial andlateral contour profiles. But the number of curves utilized to match theoverall contour profile varies between ethnicities. For example, asshown in FIG. 14 , three curves can be used to match the overall contourprofiles 164, 166. In contrast, as shown in FIGS. 15 and 16 , fourcurves are required to match the overall contour profiles 164, 166 forCaucasians and African Americans.

Referencing FIGS. 17 and 18 , the curvature of the distal femur template160 is captured using a surface sampling operation referred to herein asa “chopper.” Two choppers, one 168 rotating about a common axisextending laterally through the distal femur template to create wedgeshape slices 170 and a second extending horizontally to create slices172 having a uniform thickness, are implemented within the softwarepackage. The first rotating chopper 168 operates by rotating a planeabout the transepicondylar axis 174 of the femur template 160. Thedistal surface points of the femur template are sampled every 10 degreeswhere the chopper plane intersects the bone surface, yielding points 176collectively representative of the articulating surface curvature of thefemur template 160. The horizontal chopper, in contrast to the firstchopper, moves along a vertical axis and samples peripheral surfacepoints in defined vertical 5 mm increments along the vertical axis,which yields points 178 collectively representative of the peripheralsurface of the femur template.

Referring to FIGS. 19-29 , after the medial profile 164, lateral profile166, and contours are extracted from the femur template 160, thecontours generated by the rotating choppers 168 are parameterized withthe medial and lateral profiles to create the articulating surface ofthe template implant. As shown in FIG. 19 , to parameterize thecontours, arcs 180 are fit to the points comprising each contour. Aftereach contour is parameterized, the articulating surface 182 of theimplant is generated by using the medial and lateral profiles 164, 166to fill in the gaps between the contours, thereby resulting in a finalimplant 184. The same process is used to create all of the implants foreach ethnicity (Caucasian, Asian, African American) and gender. Eachfemur template 160 may be used to create a total 184, partial 188,and/or unilateral implant 190 such as those shown in FIGS. 25-27 .Moreover, the femoral implant may be created in as a cruciate retainingor a posterior stabilized version 186. And the inner surface of the masscustomized femoral implant, which contacts the distal femur, may beeither rectangular 192 or trapezoidal 194 (that is bone sparing).

Referencing FIGS. 30-34 , the tibial implant (whether mass customized orpatient specific) is divided into the tibial tray and the tray insert.The tray insert is generated from a tibia template 206. To generate thetibia template 206, representative of the condyle bearing surface shapesof the patient's tibia, the tibial surface 198 of the patient isanalyzed by the software package's atlas 130 to create a plane 200 atthe level of a tibial resection as shown in FIG. 33 . The softwarepackage then samples points on the surface of the tibia where this planeintersects the tibial surface as shown in FIG. 34 , resulting in thedata points 202 outlining the periphery of the tibia at the location ofthe plane. The group of points 202 created from the resection plane iscalled the resection profile.

Referring to FIGS. 35-38 , the resection profile 202 is then fit withcurves to create a parameterized profile 204, such as shown in FIG. 35 .The tibia template 206 is then generated from the parameterized profile204 as shown in FIGS. 36-38 for three ethnicities. The inside edge anddepression of the tibial template 206 are made to match a tibial tray(not shown). The tibial template is available as a unilateral componentor as a total component.

Referencing FIGS. 39-51 , the articulating surfaces of the tibialtemplate 206 are analyzed by first processing them with the horizontalchopper to sample the surfaces as a set number of points, such as shownin FIG. 39 , to generate a series of points 208 representative of thecontours of the articulating surfaces. The articulating surfaces of thetibial template 206 are then each divided into six regions 210 fit byrespective curves 212-222, as shown in FIGS. 39-45 . The curvesparameterize the tibial template 206 articulating surfaces so that thetibial tray insert 224 may be generated, as shown in FIG. 46 . The trayinsert 224 may be created for total 226 (see FIGS. 47 and 48 ) or forunilateral 228 (see FIGS. 49-51 ) tibial implants. The medial trayinsert component 224A is created from curve regions 1, 2, and 3 whilethe lateral tray insert 224B component is created from curve regions 4,5 and 6 (see FIG. 49 ). The total tray insert is generated from all sixcurve regions. The total tray insert 226 is also available for posteriorstabilized (see FIG. 48 ) and cruciate retaining (see FIG. 47 ) kneesystems.

Referring to FIG. 52 , a similar process 230 to the one describedpreviously for creation of mass customized implants is used to createpatient specific implants. While the mass customized implant processuses the patient's bones to determine the size of the implant to beassigned, the patient specific process 230 generates the implantdirectly from the patient's bone (i.e., bone model). As shown in FIG. 52, the patient's bones are added to the software package's atlas 232,where the atlas calculates the measurement landmarks for each bone. Thecalculated landmarks are used to create the implant box 234, which isthe inner surface of the implant that contacts the patient's resectedbone. The articulating surface of the patient's bone is analyzed 236 toextract the patient's bone curvature and profile information. The methodof curvature analysis is the same as that used to create the masscustomized implants and will not be repeated for purposes of furtheringbrevity. The patient's bone curves and profiles are then parameterized238 to generate the implant's articulating surfaces for both the femoraland tibial components. The calculated patient specific implant box 234and articulating surfaces are combined 240 with the articulatingsurfaces to create the final patient specific implant 242.

Referring to FIGS. 28, 29, 53, and 54 , by way of explanation, thefemoral component inner box of the patient specific implant may berectangular, trapezoidal, or contoured to match the patient's resecteddistal femur, as shown in FIG. 54 . As discussed in more detailhereafter, novel instrumentation and techniques were developed toprovide the contoured distal femur resection (that includes cartilageremoval) to accept the inner surface of the contoured patient specificimplant.

Referencing FIGS. 55 and 56 , the patient specific instrumentation comesin two varieties. The first variety, a free form femoral cutting guide250 (see FIG. 55 ), controls the motion of a standard surgical drillalong a pair of tracks. The shape of the tracks is derived from theprofiles and contours of the patient's femoral anatomy. The secondvariety, a microsurgical robot guide 252 (see FIG. 56 ), is a moreadvanced instrument that makes use of a microsurgical robot 254 that isaware of its position with respect to the femur. The microsurgical robotguide 252 makes use of a physical track to guide motion of themicrosurgical robot 254 from the anterior to posterior of the femur.Like the free form femoral cutting guide 250, the track of themicrosurgical robot guide 252 is generated from the profiles of thepatient's femur. As the microsurgical robot 254 travels over the surfaceof the femur, it adjusts its cutting depth to follow the contour of thefemur, allowing the cartilage and some bone to be removed.

Referring to FIGS. 55 and 57-63 , the free form femoral cutting guide250 serves as a non-powered framework to guide a standard surgical drill256 along an anatomically defined pathway that results in removal ofcartilage 258 from the distal femur 260 thereby leaving a resurfacedportion 262 suitable for a conformal femoral implant. After thepatient's femoral bone model has been generated, the software packageuses this femoral bone model to generate the free form femoral cuttingguide 250. The free form femoral cutting guide 250 is mounted to abone-mounted base component 264, which is positioned with respect to thepatient's femur 260 using a patient specific jig. To prepare thepatient's distal femur 260 to accept the orthopaedic implant, thesurgeon slides the surgical drill 256 along a pair of interlockedtracks. A first track 266 controls motion in the anteroposterior (AP)direction (see FIG. 59 ) and a second track 268 controls motion in themediolateral (ML) direction (see FIG. 60 ). Combining both motionsresults in the removal of cartilage from the area of the distal femur260 for unilateral (see FIGS. 61 and 62 ) or total (see FIG. 63 ) kneearthoplasty.

The free form femoral cutting guide 250 includes several components.Among these components are: (1) a segmented femur with cartilage model270; (2) a medial AP track; (3) a medial ML track; (4) a lateral APtrack; (5) a lateral ML track; (6) a sulcus AP track; (7) a sulcus MLtrack; (8) a track slider; (9) a fixation arm; (10) a base component;and, (11) a patient specific jig.

Referring to FIGS. 57 and 58 , an exemplary process 300 for constructingthe femur with cartilage model 270 starts with using any number ofimaging modalities as a data source 302 including, without limitation,CT, X-rays, and MRI. To create the femur with cartilage model 270 usingMRI, a scan of the patient's knee is acquired from which DICOM files areobtained. These DICOM files (that include bone and cartilage) are thenautomatically segmented 304, 306 (i.e., sliced) by the software packageto create surface models of the patient's femur. The surface models arethen added to a principal component-based statistical bone atlas togenerate the femur with bone cartilage model. This femur with cartilagebone model may be added to the atlas and used to generate the necessaryprofiles without further processing.

To create the femur with cartilage model using CT images, the patient'sknee is scanned and the resulting DICOM files are obtained. These DICOMfiles are automatically segmented 310 by the software package. Butbecause cartilage information is not captured in CT images, additionalprocessing is required to estimate this tissue, which will be discussedhereafter.

To generate a femur with cartilage model using X-rays, the patient isfitted with a registration brace and then bi-planar X-rays are taken ofthe patient's knee. Thereafter, an X-ray bone reconstruction task 312 iscarried out that includes creation of the surface model of the patient'sbone from bi-planar X-rays. This task includes taking the X-ray imagesand an average bone from a principal component based statistical boneatlas and placing them in a three dimensional (3D) scene. An initialpose is then defined by a user of the software package and the averagebone shape, translation, and rotation are optimized through a geneticalgorithm and 2D-to-3D scoring metric. After convergence is reached, theresultant surface model generated from the atlas model is representativeof the patient's femoral geometry. As with CT, additional processing isrequired to estimate the patient cartilage.

X-ray and CT modalities require a cartilage reconstruction process 314to generate an estimated cartilage model to be applied to the distalfemur surface model. This cartilage model is derived from cartilagetissue segmented from MRI data. After the femoral surface model of thepatient has been created, the cartilage model is scaled by the softwarepackage to fit the patient's femoral surface model and then applied tothe femoral surface model. After cartilage is added to the femoralsurface model, AP profiles and ML contours may then be generated by thesoftware package.

A more detailed discussion of some of the features shown in FIGS. 57 and58 may be found in U.S. patent application Ser. No. 13/203,010,entitled, “INTELLIGENT CARTILAGE SYSTEM,” the disclosure of which isincorporated herein by reference.

Referring to FIG. 64 , in order to prepare the patient's distal femur260 to receive the orthopaedic implant, the distal end of the femur mustbe processed. Processing of the distal femur includes recontouring thedistal end of the femur 260 to remove certain cartilage, thus allowingthe orthopaedic implant to directly contact bone. In order to begin thisprocess, a base 360 is mounted to the anterior femur 260, proximate thedistal end. This base 360 provides a foundation to which the guides ofthe cutting tool are mounted. In exemplary form, the base 360 comprisesa rectangular block (six sided) having a through cavity 362 with arectangular cross-section that extends from the medial side to thelateral side. As will be discussed in more detail hereafter, the throughcavity 362 is adapted to accommodate insertion of at least a portion ofa horizontal arm 364. The base 360 also includes three through cavities366, 368, each having the same circular cross-section and orientednormal to the rectangular through cavity. The three through cavities366, 368 are oriented along a diagonal line that extends across opposingtop and bottom surfaces of the base. The through cavities 366 at the endof the diagonal line are adapted to accept bone screws 370 that operateto couple the base 360 to the anterior femur 260. The middle throughcavity 368 is adapted to receive a set screw 372 used to lock thehorizontal arm 364 within the rectangular through cavity 362.

In this exemplary embodiment, the base 360 is fabricated from highdensity polyethylene. But those skilled in the art will realize theother materials may be used to fabricate the base including, withoutlimitation, titanium, stainless steel, ceramics, and other biologicallyinert materials.

In order for the base 360 to be useful during the cutting process, thebase must be mounted to the anterior femur 260. In order to accuratelyposition the base 360 with respect to the femur 260, a patient-specificplacement guide 374 is created by the software package that includes apair of arcs 376, 378 that are shaped to overly and match the patient'snative distal femur (i.e., matches the distal articulating surfaces ofthe condyles and cartilage) with the native cartilage in place. Botharcs 376, 378 are tied together via a cross-brace 380, as well as thefact that the arcs converge proximate the anterior femur. Where the arcs376, 378 converge, the patient-specific placement guide 374 includes aboxed-in frame 382 that faces toward the anterior femur 360 and includesa through opening 384. More specifically, this boxed-in frame 382 issized to accommodate partial insertion of the base 360 and retain thebase in position against the anterior femur 260.

Referencing FIGS. 65 and 66 , in exemplary form, the patient-specificplacement guide 374 is positioned to contact the distal femur 260 sothat each arc 376, 378 contacts a respective condyle (and itscartilage). The rotational and lateral position of the patient-specificplacement guide 374 is fixed because only one position is operative toalign both arcs 376, 378 with their respective condyles so that theinternal circumferential surface of each arc is in continuous contactwith a respective condyle. Prior to reaching this position, the base 360is loaded into the boxed-in frame 382 so the three through cavities 366,368 are accessible via the through opening 384 of the boxed-in frame. Inthis manner, when the arcs 376, 378 are positioned onto the condyles andaligned, the anterior femur 260 and boxed-in frame 382 are operative tosandwich the base 360 therebetween. At the same time, thepatient-specific placement guide 374 orients the base 360 properly withrespect to the anterior femur 260 so that a surgeon may drill holes intothe anterior femur using the top and bottom circular through cavities366 at the end of the diagonal line as drill guides. Thereafter, bonescrews 370 are inserted into the top and bottom circular throughcavities 366 and extended to engage the anterior femur 260, therebysecuring the base to the femur. Subsequently, the patient-specificplacement guide 374 is removed and the base 360 remains mounted to theanterior femur 260.

As shown in FIGS. 3.4-3.7 , after the base 360 is mounted to theanterior femur 260, the horizontal arm 364 is inserted into the throughopening 362. In this exemplary embodiment, the horizontal arm 364comprises a stem having a rectangular cross-section that allows the stemto be inserted into the through opening 362 of the base 360. At one endof the arm 364 is an eyelet 386 that defines a through opening 388having a constant rectangular cross-section. In this exemplaryembodiment, through opening 388 extends perpendicularly with respect tothe longitudinal length of the arm 364. The eyelet 386 also includes asecond opening 390 that extends through a side of the eyelet. Thissecond opening 390 is concurrently perpendicular to the longitudinallength of the arm 364 and to the axial direction of the rectangularthrough opening 388. More specifically, the second opening 390 iscylindrical in shape, defined by a constant circular cross-section, thatextents through a side of the eyelet 386 and into the rectangularthrough opening 388. In exemplary form, the second opening 390 isadapted to receive a set screw 392 that concurrently contacts a siderail/track 394 in order to mount the side track to the horizontal arm364.

The side track 394 comprises a medial AP track, a lateral AP track, andan anterior AP track that has a profile that matches the intendedprofile of the distal femur 260 post resurfacing. As will be discussedin more detail hereafter, the intended profile is generatedautomatically by the software package after creation of the patient'sfemoral bone using images from one or more modalities. In this exemplaryembodiment, each side track 394 comprises solid rectangular bar stockhaving a rectangular cross-section between a first end and a second end.In other words, the side track 394 includes a top surface 396 and abottom surface that are parallel to one another and separated from oneanother by a pair of side surfaces 398. In this exemplary embodiment, itis the top surface 396 that embodies the intended profile of the condyleor anterior femur 260 after resurfacing. Each side track 394 alsoinclude a pair of cylindrical cavities formed into one or both sidesurfaces to accept a stop 400, such as a screw, to limit travel of acarriage assembly 402.

Referring to FIGS. 69, 70, and 101 , the carriage assembly 402 comprisesa top follower 404 and a bottom follower 406 that are coupled to oneanother by a pair of screws 407 that extend vertically and outset fromthe side surfaces 398 of the side track 394. The bottom follower 406 isgenerally rectangular in cross-section and includes a flat bottomsurface and a contoured top surface. This top surface is notched out toaccommodate partial insertion of the side track 394 so that the topsurface defining the notch is adjacent the bottom surface of the sidetrack. More specifically, the rectangular notch is slightly larger thanthe width of the side track 394 to ensure that the bottom follower 406can move along the side track 394, but the notch is not so wide as toprovide significant play that would change the angular pitch of thebottom follower as it is repositioned along the track. Outset from thenotch, on both sides, is a pair of cavities sized to receive screws 407that operate to couple the top follower 404 to the bottom follower 406.The top follower 404 is likewise notched to accommodate partialinsertion of the side track 394. More specifically, the top follower 404includes a rectangular notch on its bottom side that includes a widththat is slightly larger than the width of the side track 394 to ensurethat the top follower can move along the side track, but the notch isnot so wide as to provide significant play that would change the angularpitch of the top follower as it is repositioned along the track. Outsetfrom the notch in the top follower 404, on both sides, is a pair ofcavities sized to receive screws 407 that concurrently are receivedwithin the cavities of the bottom follower 406 in order to mount thefollowers to one another. In exemplary form, the screws 407 aretightened so that the vertical distance between the bottom of the notchfor the bottom follower 406 and the top of the notch for the topfollower 404 is larger than the distance between the top 396 and bottomsurfaces of the side track 394. In this manner, there is play in betweenthe followers 404, 406 and side track 394 in the vertical direction,which allows the followers to be repositioned along the length of theside track.

A contour track 408 is mounted to the top follower 404. In exemplaryform, contour track 408 includes a mounting platform having a pair ofthrough openings aligned with the through openings of the top follower404. In this manner, screws 407 inserted through the openings of themounting platform and the top follower 404 are operative to extend intocommunication with the bottom follower 406 and mount the followers andthe contour track 408 to one another. In this exemplary embodiment, themounting platform comprises a rectangular housing that is generallyconstant along the length and width of the housing. The top of themounting platform includes the pair of through openings extending intocommunication with the openings of the top follower 404.

In exemplary form, the contour track 408 comprises three segments thatare individually, but not concurrently, mounted to the top follower 404to define the medial to lateral path of the cutter. These three segmentscomprise a medial ML track 408A, a lateral ML track 408B, and ananterior ML track 408C. As will be discussed in more detail hereafter,each segment of the contour track 408 is utilized by the cutting tool toresurface a portion of the distal femur 260. For example, the medial MLtrack 408A acts as a medial-to-lateral guide for the cutting tool whencutting the medial condyle (see FIG. 68 ), until reaching the pointwhere the condyles converge interiorly, where the anterior ML track 408Cis utilized as a medial-to-lateral guide for resurfacing the anteriorportion of the distal femur (see FIG. 70 ). Similarly, the lateral MLtrack 408B is utilized by the cutting tool as a medial-to-lateral guidefor resurfacing the lateral condyle (see FIG. 69 ).

Referring to FIG. 71 , the profile of each side track 394 is generatedby the software package using the using the medial 410, lateral 412, andsulcus 414 profiles of the patient's distal femur 260. As discussedpreviously, the medial and lateral profiles 410, 412 are generated withrespect to a plane having within it three points: the most anteriorpoint, the most distal point, and the most posterior point of eachcondyle with cartilage in place. The outermost points on the bone 260(exterior surface) that fall within a respective plane are resampled tocreate a 2D profile consisting of fifty equidistant points, therebycreating a medial profile 410 for the medial condyle and a lateralprofile 412 for the lateral condyle. The sulcus profile 414 iscalculated by rotating a plane about the TEA in ten degree incrementswith respect to the distal femur 260 (with cartilage in place). Thepoints where the plane intersects the bone surface are captured,creating a series of contours in the mediolateral (ML) direction thatare offset by ten degrees. For each contour, the lowest point of the MLcontour defines the sulcus location. The sulcus locations/points arecompiled in 2D to create a sulcus profile 414.

Referencing FIGS. 71-76 , a process for constructing the medial sidetrack 394A includes taking the 2D profiles 410, 414 of the medialcondyle and sulcus so that the medial side track has a posterior profilethat matches precisely the 2D profile of the medial condyle and ananterior profile that matches precisely the sulcus profile. In otherwords, the medial side track 394A is defined posteriorly by the medialprofile 410 and anteriorly by the sulcus profile 414. The medial sidetrack 394A provides a guide in an X-Y plane, while the contour track 408provides a guide in a Y-Z plane with respect to the medial condyle. Thecurvature of the sulcus is used to create the anterior portion of themedial side track 394A because using only the medial profile of thedistal femur results in unsatisfactory resurfacing of the anteriordistal femur 260. The software program is operative to combine thecurvatures of the posterior medial profile 410 (see FIG. 73 ) and thesulcus profile 414 (see FIG. 74 ) to create a single curve (see FIG. 75) that embodies the intended final curvature of the medial side track394A (see FIG. 76 ).

Referring to FIGS. 71, 77-79 , a process for constructing the lateralside track 394B includes taking the 2D profile for the lateral condyle412 so that the lateral side track has a profile that matches preciselythe 2D profile of the lateral condyle. The lateral side track 394Bprovides a guide in an X-Y plane, while the contour track 408 provides aguide in a Y-Z plane with respect to the lateral condyle.

Referring to FIGS. 71 and 80-83 , a process for constructing theanterior side track 394C includes taking the 2D profile for the sulcusand using the software package to extrapolate the profile 414 outward(see FIG. 81 ) to increase the size of the curve so that the anterior APside track created from the sulcus curvature is similar in size to themedial and lateral AP side tracks (see FIG. 82 ). The anterior AP sidetrack 394C provides a guide in an X-Y plane allowing the cuttinginstrument to remove the cartilage remaining after application of thelateral AP side track 394B and the medial AP side track 394A.

Referencing FIGS. 84-88 , the medial ML track 408A guides the cuttinginstrument in the Y-Z plane (i.e., in the medial-to-lateral direction)across the surface of the distal femur 260. As mentioned previously, thepatient's femur 260 is modeled to create a virtual, 3D bone that thesoftware package uses to extract the contour of the patient's distalfemur and construct a virtual jig (in this case the medial ML track)that is output to a CNC machine for fabrication of the actual medial MLtrack 408A. The software package initially takes the patient's virtual,3D bone and generates the medial 416, lateral 418, and sulcus 420contours by rotating a plane about the TEA in ten degree increments tocreate a point cluster 422 of the external surface of the distal femur(see FIG. 85 ). The surface points 422 corresponding to cartilage aresampled and the regions of interest are split between the anterior femur(FIG. 86 ) and posterior femur (FIGS. 87 and 88 ) due to variabilitybetween the two regions. In this exemplary discussion, the anterior areaof interest is limited to the three contours 424 and the posterior areais also limited to three medial-to-lateral contours 426, 428.

Referring to FIGS. 89-94 , the acceptable points 422 of the contours424-428 are collapsed towards a single plane (see FIGS. 89, 90, 92, and93 ). It is achieved by rotating them towards an arbitrary common planeabout the TEA. This process produces a parametric curve by calculatingthe best fit of the anterior and posterior contour sets (see FIGS. 91and 94 ).

Referring to FIGS. 95-100 , the curve fit 430 to the medial contourpoints 424 is used to define the medial ML track 408A, the curve 432 fitto the lateral contour points 426 is used to define the lateral ML track408B, and the curve 434 fit to the anterior contour points 428 is usedto define the anterior ML track 408C.

Referencing FIGS. 55, 106, and 107 , the patient-specific placementguide 374 is shown mounted to the patient's distal femur 260 with themedial AP side track 394A mounted to the base 360 via the arm 364. Insuccession, the medial ML track 408A, lateral ML track 408B, andanterior ML track 408C are mounted to the medial AP side track 394A toguide the cutting instrument to resurface the medial and lateralcondyles, as well as the anterior portion of the distal femur 260.

Referring to FIGS. 101-105 , in operation, the cutting tool 256 iscoupled to the patient-specific placement guide 374 in order tofacilitate relatively small incremental movements in theanterior-posterior direction and larger movements in the medial-lateraldirection. More specifically, as discussed above, one of the medial,lateral, or anterior ML track 408 is repositionably mounted to a side APtrack 394 to facilitate guided movement in the anterior-posteriordirection. The cutting tool 256 is repositionably mounted to therespective ML track 408 that is mounted to the side AP track 394. Inthis manner, the cutting tool 256 can be repositioned in themedial-lateral direction to remove cartilage 258 (and possibly somebone) to create a cutting profile having a constant depth that matchesthe associated medial, lateral, or anterior ML track 408 mounted to thecutting tool. After the cutting tool 256 has completed a medial-lateralswath, the cutting tool is repositioned in the anterior-posteriordirection to cut another swath that slightly overlaps the previous swathto ensure complete coverage between sequential swaths. This process isrepeated until the entire area of the distal femur is cut that isintended to be cut with the respective ML track 408. Thereafter, adifferent ML track 408 is installed and the process repeated for this MLtrack. Thereafter, the process is repeated for the final ML track 408.

The goal of the cutting process is to remove cartilage 258 from thedistal femur 260. Of concern is the possibility of excessive gouginginto the bone during cartilage removal. Slight grazing of the bone 260is almost unavoidable because the cutting depth is maintained as aconstant depth. Nevertheless, gouging may be eliminated by reducing thecutting depth. But reductions in cutting depth also reduce the overallthickness of the cartilage 258 removed and may result in too muchcartilage being retained. The ideal circumstance is to have minimal bonegrazing and maximum cartilage removal. In order to provide the propercutting depth for each ML track 408, a simulation is preformed by thesoftware package to quantitatively test the amount of gouging into thebone 260 by comparing a simulated cutting pathway at a particular depthto the patient's bone model without cartilage.

The simulation is performed by sweeping each ML track 408 along its APpathway, as defined by the relevant AP side track 394. The simulationassumed all portions of the patient-specific placement guide were rigidwith rigid connections between the ML tracks 408 and AP side track 394and the holster coupling the cutting device to a respective ML track.The angles between the AP side track 394 and ML tracks 408 were assumedto be perpendicular at all times in the coronal plane. It should benoted that vibration of the cutting device was not accounted for in thesimulation.

For each ML track simulation, the ML track 408 was translated along theAP side track 394 until the ML track made contact with the bone surface.After reaching the depth where the ML track 408 contacted bone, therespective ML track was then swept along its respective AP side track394 to generate both a sheet body and a solid cutting body. The sheetbody comprises a very thin sheet (vertically thin) that conforms to theundersurface of the cartilage 258 and bone 260 post cutting. This sheetbody is used to assess the amount of gouging into the bone that occursas any bone contacting the sheet indicates a gouge. The solid bodycomprises a three dimensional object made up of the amount of materialto be removed by the cutting tool as the cutting tool is moved in themedial-lateral direction for a respective ML track 408. The solid bodywas generated by Boolean subtraction method using the femur model withcartilage and the femur model post cutting. After all cuts from the MLtracks 408 were simulated, the resultant femur and separated cartilagerepresenting the result of a TKA preparation was imported into Amira 3.0and the cuts were assessed through a distance map between the cartilagesurface and processed femur surface.

Referring to FIG. 108 , it was observed during the simulation that whileno bone is being gouged using the medial ML track at a firstpredetermined depth, there is a noticeable gap to the anterior surface.To address this anterior gap and possibly increase the amount ofcartilage removed, the simulation was again carried out, but this timewith the medial ML track being lowered by one millimeter.

Referencing FIGS. 109 and 110 , the anterior and distal views of thedistal femur with the sheet body in place show that the anterior gap islessened, but that some grazing of the bone occurred. Based upon thecomparison between the medial ML track simulations, a surgeon may raiseor lower the medial ML track with respect to the side AP track.

Referring to FIGS. 111-113 , the side AP track is shown positioned withrespect to the medial ML track. The computer program evaluates the swathcreated by the cutting tool and creates the sheet body superimposed ontothe distal femur with cartilage in place. In this circumstance, thesheet body provides an observer with and indication of the amount ofcartilage removed as all cartilage above the sheet body would beremoved. At the same time, the software program is capable of generatingthe solid body superimposed onto the distal femur with cartilage to showthe three dimensional cutting route of the cutting tool.

Referencing FIGS. 114 and 115 , anterior and posterior views of thefemur as part of the simulation carried out by the software packagerepresent the femur with cartilage and without cartilage post cutting.As can be seen in these figures, the resulting bone is generally smoothand lacks cartilage on the bearing surfaces of the medial condyle. Itwas observed during the simulation that while no bone is being gougedusing the lateral ML track at a first predetermined depth, there is anoticeable gap to the anterior surface. To address this anterior gap andpossibly increase the amount of cartilage removed, the simulation wasagain carried out, but this time with the lateral ML track being loweredby two millimeters.

Referencing FIGS. 116 and 117 , the anterior and distal views of thedistal femur with the sheet body in place show that the anterior gap islessened, but that some grazing of the bone occurred. Based upon thecomparison between the lateral ML track simulations, a surgeon may raiseor lower the lateral ML track with respect to the side AP track.

Referring to FIGS. 118-120 , the side AP track is shown positioned withrespect to the lateral ML track. The computer program evaluates theswath created by the cutting tool and creates the sheet bodysuperimposed onto the distal femur with cartilage in place. In thiscircumstance, the sheet body provides an observer with and indication ofthe amount of cartilage removed as all cartilage above the sheet bodywould be removed. At the same time, the software program is capable ofgenerating the solid body superimposed onto the distal femur withcartilage to show the three dimensional cutting route of the cuttingtool.

Referencing FIGS. 121 and 122 , anterior and posterior views of thefemur as part of the simulation carried out by the software packagerepresent the femur with cartilage and without cartilage post cutting.As can be seen in these figures, the resulting bone is generally smoothand lacks cartilage on the bearing surfaces of the lateral condyle.

Referring to FIGS. 123-126 , it was observed during the simulation thatan acceptable amount of bone was gouged using the anterior ML track at afirst predetermined depth. Accordingly, no additional simulation at adifferent cutting depth was necessary or attempted. The anterior view ofthe distal femur is created as part of the software package representingthe femur pre and post cutting. As can be seen in this figure, theresulting bone is generally smooth and lacks cartilage on an anteriorbearing surface.

Referencing FIGS. 127-129 , the software package is operative to createa femur having been cut using each of the medial, lateral, and anteriorML tracks. Overall, the combined ML tracks graze the femur in someareas. But the anterior fit is very close and all cuts come togetherevenly. All combined cuts cover the total area of the bearing surfacesto remove the cartilage as part of a total knee arthroplasty (TKA)procedure.

Referring back to FIG. 56 and forward to FIGS. 130 and 131 , anexemplary microsurgical robot guide 252 is an advanced instrument thatincludes a microsurgical robot 254 that is aware of its position withrespect to the distal femur 260. The microsurgical robot guide 252 makesuse of the same side AP track 394 as the free form femoral cutting guide250 to guide the microsurgical robot's 254 motion from the anterior toposterior of the femur 260. Like the free form femoral cutting guide250, the AP track 394 is generated from the profiles of the patient'sfemur 260. As the microsurgical robot 254 travels over the surface ofthe femur in the medial-lateral direction, it adjusts its cutting depthto follow the contour of the femur, allowing the cartilage to beremoved. The microsurgical robot 254 creates a cartilage resectionconformal to the distal femur surface. The resulting resection issuitable for a conformal patient specific implant, which may beunilateral, bilateral, or trilateral.

Referencing FIGS. 55 and 56 , preparation for using the microsurgicalrobot guide 252 is similar to that of the free form femoral cuttingguide. Initially, a distal femur with cartilage model of the patient isobtained automatically using one or more imaging modalities such as,without limitation, CT, X-ray, and MRI. A more detailed discussion ofhow the distal femur with cartilage model is created from imagingmodalities has been previously recited herein and will not be repeatedfor purposes of brevity.

As with the free form femoral cutting guide 250, the microsurgical robotguide 252 makes use of the same base 360 and positioning template 374for securing the base onto the anterior portion of the distal femur 260.For a more detailed discussion of the base and use of the positioningtemplate, reference is had to the free form femoral cutting guide 250section. After the base 360 has been positioned, the side AP track 394is mounted to the base, precisely as it was discussed with respect tothe free formal cutting guide 250. But what is different from the freeform femoral cutting guide 250 is that the microsurgical robot guide 252obviates the need to generate separate medial, lateral, and anterior MLtracks. Instead, the microsurgical robot guide 252 includes amicrosurgical robot 254 programmed with the contours of medial, lateral,and anterior ML tracks.

Referring to FIGS. 130-136 , the microsurgical robot guide 252 comprisesa support frame 450 that is mounted to the side AP track 394 to providea platform for the robot 254 to translate in the ML and proximal-distal(PD) directions. The support frame 450 includes a pair of spaced apartvertical supports 452 that straddle the side AP track 394. Two dowels454 extend between and are concurrently mounted to the vertical supports452. In exemplary form, the dowels 454 are vertically spaced apart fromone another slightly more than the vertical thickness of the side APtrack 394. In this manner, the dowels 454 sandwich the side AP track 394in the PD direction, while the vertical supports 452 sandwich the sideAP track 394 in the ML direction. This four sided constraint onlyprovides freedom of movement of the support frame 450 along the lengthof the side AP track 394.

In addition to the dowels 454, a rectangular elongated support 456 isconcurrently mounted to the vertical supports 452. More specifically,the rectangular elongated support 456 has a constant rectangularcross-section and has a linear longitudinal dimension. In this exemplaryembodiment, the elongated support 456 is mounted at one end to the firstvertical support 452 to extend perpendicularly therefrom. The secondvertical support 452 includes a rectangular opening through which theelongated support 456 extends. In this orientation, the elongatedsupport 456 is perpendicular with respect to the vertical supports 452and also perpendicular with respect to the side AP track 394. No matterhow the elongated support 456 is positioned with respect to the side APtrack 394, the elongated support extends perpendicularly away from theside AP track. To ensure the elongated track 456 maintains thisorientation with respect to the side AP track 394, the side AP track andthe support frame are fabricated from a non-elastomeric material suchas, without limitation, a metal, a metal alloy, a ceramic, and athermoset polymer. The first vertical support 452 also includes anopening 458 adapted to accommodate a control arm 460.

The control arm 460, in exemplary form, comprises a handle 464 coupledto a straight, cylindrical shaft 466. The control arm 460 isrepositionable in the ML direction because the diameter of thecylindrical shaft 466 is less than the diameter of the circular opening458 in the first vertical support 452 through which it extends. A firstend of the cylindrical shaft 466 is mounted to the handle 464, which islocated on a first side of the vertical support 452, while the secondend of the cylindrical shaft is mounted to a robot housing 470. Therobot housing 470 includes a servo motor (not shown) coupled to arotating cutting tool 472, in this case a drill bit. The servo motor isoperative to reposition the drill bit 472 in the PD direction responsiveto changes in position of the drill bit with respect to the distalfemur.

The location of the drill bit 472 is tracked in the AP direction via alinear cable extension transducer (not shown). The output voltage of thetransducer varies as the length of cable drawn from the transducerchanges. The transducer is connected to reference points on the supportframe 450 and the AP track 394. As the robot 254 is translated along theside AP track 394, the output voltage of the transducer accordinglychanges and the position of the robot is known. Similarly, the locationof the robot 254 in the ML direction is also determined by a linearcable extension transducer (not shown). The transducer is connected toreference points on the support frame 450 and the robot housing 470.Accordingly, the robot 254 is aware of its position with respect to thedistal femur 260, which allows the robot to accurately remove softtissue with minimal effort required from the surgeon.

The cutting depth of the drill bit 472 is determined by the softwarepackage using constructed virtual 3D models of the distal femur 260after cutting and prior to cutting with cartilage. Using the subtractionof these two models, the resultant is a 3D model of the patient's tissueto be removed with dimensions in 3D. As a result, the robot 254 isprogrammed to contour the underlying bone by using the three dimensionalmodel of tissue to be removed. As discussed previously, the softwarepackage is operative to generate mediolateral contours of the distalfemur 260 by rotating a plane about the TEA in increments of tendegrees. The cartilage surface points are sampled where this planeintersects the cartilage. The software package then analyses themediolateral contours and generates a contour map of the articulatingsurface along with the corresponding cartilage thickness.

To use the microsurgical robot guide 252, the surgeon moves the supportframe 450 with respect to the side AP track 394 to reach a startingposition. Thereafter, the surgeon manipulates the handle 464 toreposition the robot housing 470 in the ML directions to remove apredetermined amount of cartilage. As the handle 464 and, thus, therobot housing 470 are repositioned in the ML direction, the robot 254 isoperative to track the position of the drill bit 472 with respect to theposition of the distal femur 260. In this manner, the robot 254 controlsthe server motor to extend the drill bit 472 to create a deeper cut andto retract the drill bit to create a shallower cut. After the surgeonhas cut a ML swath, the support frame 450 is moved anteriorly orposteriorly in order for the bit 472 to make another swath and removecartilage in the ML direction. This same process is repeated until theentire distal end of the femur is resurfaced.

Following from the above description and invention summaries, it shouldbe apparent to those of ordinary skill in the art that, while themethods and apparatuses herein described constitute exemplaryembodiments of the present invention, the invention contained herein isnot limited to this precise embodiment and that changes may be made tosuch embodiments without departing from the scope of the invention asdefined by the claims. Additionally, it is to be understood that theinvention is defined by the claims and it is not intended that anylimitations or elements describing the exemplary embodiments set forthherein are to be incorporated into the interpretation of any claimelement unless such limitation or element is explicitly stated.Likewise, it is to be understood that it is not necessary to meet any orall of the identified advantages or objects of the invention disclosedherein in order to fall within the scope of any claims, since theinvention is defined by the claims and since inherent and/or unforeseenadvantages of the present invention may exist even though they may nothave been explicitly discussed herein.

What is claimed is:
 1. A microsurgical robot guide system comprising: a cutting guide configured to be mounted to an anatomical structure so as to be positioned relative to an articulating surface of the anatomical structure, the cutting guide including a track having a shape derived from the articulating surface; and a robot including a carriage and a cutter mounted thereto, the robot coupled to the track via the carriage so as to be displaceable along the articulating surface upon the cutting guide being mounted to the anatomical structure, the carriage displaceable relative to the track with the cutter so as to follow a pathway conforming to an implant surface.
 2. The microsurgical robot guide system of claim 1, wherein the robot is arranged for automated resurfacing of the anatomical structure along the pathway.
 3. The microsurgical robot guide system of claim 1, further comprising a control arm coupled to the track and mounted to the carriage, the control arm manually displaceable along the track so as to displace the carriage therewith relative to the track.
 4. The microsurgical robot guide system of claim 1, wherein the robot has a servo motor operatively connected to the cutter, the servo motor arranged for sensing a position of the carriage relative to the track and for selectively operating the cutter according to the position of the carriage.
 5. The microsurgical robot guide system of claim 4, wherein the servo motor is configured so as to extend or retract the cutter relative to the carriage based on the position of the carriage.
 6. The microsurgical robot guide system of claim 4, wherein the servo motor is arranged for sensing a position of the cutter relative to the anatomical structure and to be controllably operable responsive to changes to the position of the cutter.
 7. The microsurgical robot guide system of claim 1, wherein the cutter is a rotatable drill bit.
 8. The microsurgical robot guide system of claim 1, wherein the cutting guide has a base joined to the track, the base adapted to be fastenable to the anatomical structure proximate the articular surface, the cutting guide configured to be mountable to the anatomical structure via fastening of the base thereto.
 9. The microsurgical robot guide system of claim 8, further comprising a placement guide including a frame connectable to the base and an alignment portion connected to the frame and having a shape matching that of the articulating surface, the placement guide being configured such that the base is positioned relative to the articulating surface upon the alignment portion being overlaid onto the articulating surface and the base being connected to the frame.
 10. The microsurgical robot guide system of claim 9, wherein the placement guide is configured such that upon the base being positioned relative to the articulating surface via the frame, the base is fastenable to the anatomical structure, and to be removable from the anatomical structure upon the frame being connected to the base fastened to the anatomical structure.
 11. The microsurgical robot guide system of claim 10, wherein the placement guide is configured for positioning the base relative to the articulating surface such that upon the cutting guide being mounted to the anatomical structure, the cutter is displaceable so as to follow the pathway unhindered.
 12. A robotic surgery system comprising: a robot including a cutter and a guiding structure, wherein: the cutter being displaceably mounted to the guiding structure; the guiding structure configured to provide a tool path along which the cutter is three dimensionally displaceable relative to the guiding structure; and the guiding structure configured to be positioned relative to a bone with cartilage such that the tool path intersects the bone with cartilage; and a control device including a software package operative to control the robot, the software package configured for processing a model of the bone with cartilage and a model of the tool path, the software package configured to define: a selected patient-specific positioning of the guiding structure relative to the bone with cartilage, in which a portion of tissue to be removed from the bone with cartilage is inside the tool path; a selected cutting route of the cutter along the tool path; and a three dimensional model of the portion of tissue to be removed from the bone, wherein the software package is operatively connected to the robot to displace the cutter relative to the guiding structure such that, in the selected patient-specific positioning, the cutter is displaceable along the selected cutting route so as to contour the bone with cartilage based on the model of the portion of tissue to be removed. 